Some vehicles include doors formed from a lightweight material, such as a polymer resin, a urethane resin, acrylic, or the like. Doors formed from lightweight materials may be generally lighter than doors formed from steel or aluminum, which may assist in lowering the overall weight of the vehicle and improving the vehicle's efficiency (e.g., fuel efficiency). However, doors formed from lightweight materials may be generally less rigid than doors formed from steel and aluminum, and the doors may elastically deform under forces under which a conventional door made of steel or aluminum would remain rigid. In larger vehicles including larger doors, elastic deformation resulting from torsional forces acting on the door may be amplified.
Accordingly, a need exists for structures to increase the rigidity of vehicle doors.